Field of the Invention
The present invention relates to a solid-state imaging apparatus, a method for manufacturing the same, and an imaging system.
Description of the Related Art
A solid-state imaging apparatus includes a photoelectric conversion portion (pn-junction diode) formed on a substrate and reads out charges generated by light which has been incident on the photoelectric conversion portion. Japanese Patent Laid-Open No. 2008-034836 discloses a photoelectric conversion portion which is formed by a p-type epitaxial layer provided on a substrate and an n-type epitaxial layer provided on the p-type epitaxial layer. The p-type epitaxial layer is formed such that a p-type impurity concentration decreases from the lower side to the upper side. The n-type epitaxial layer is formed such that an n-type impurity concentration increases from the lower side to the upper side. According to a structure described in Japanese Patent Laid-Open No. 2008-034836, for example, the movement in the horizontal direction of charges generated by photoelectric conversion is suppressed, thereby preventing a crosstalk between pixels.
The charges generated by photoelectric conversion can move under the influence of a potential distribution which is determined by the impurity concentration distribution of the photoelectric conversion portion. Each of the above-described n-type and p-type epitaxial layers is formed by epitaxial growth while adjusting a dopant concentration in an epitaxial growth chamber. It is not easy to accurately control the impurity concentration distribution. Hence, according to a photoelectric conversion portion formed by an epitaxial growth method, it is difficult to improve charge transfer efficiency for reading out the charges generated by photoelectric conversion.